Forms of 4-(2-quinolylazo)-resorcinol and its complex with indium

States of 4-(2-quinolazo)-resorcinol at different pH and of its complex with indium are studied by the MO LKAO Huckel method and by the method of spectrophotometry. The most probable structures of the reagent and the complex are established. The main reason of the difference in sensitivity of analytical reactions of indium ions with 4-(2-quinolylazo)-resorcinol) and 4-(4-methyl-2-pyridylazo)-resorcinol is found out